This invention relates to leak-free enclosures to support electronic device and more specifically to an enclosure construction that will allow a reduction in the overall height of the enclosure.
The electronics industry requires vast quantities of miniature enclosures to support and protect electronic crystals, transistors, and other devices. These enclosures consist of "bases" or "headers" and matching "cans" or "covers". These enclosures provide protection from atmosphere, moisture, and other factors that can degrade their performance of electronic devices. The base supports and protects the active component or components in a hermetic or leak-free environment while providing a method for signals to pass into and out of the device by means of any number of insulated wires or pins. One of the most reliable and cost-effective methods of constructing bases or headers employs the use of certain glass and metal alloys that can be bonded to each other through the use of various processes. These processes produce a "finished" base that is ready to receive the active device.
After the active device is installed, a "can" or "cover" is attached over the base to complete the enclosure. There are various methods for attaching the cover which must also form a hermetic seal with the base. Methods typically employed are: Attachment by a relatively low temperature solder, resistance welding, and cold-welding.
Each of the "closure" methods have applications, but the cold-welding method has been found to be a preferred method, especially in the electronic frequency control industry, as it neither generates nor requires heat, current, flux, or other potentially detrimental factors.
The cold-weld method as commonly used in the frequency control industry was developed in the 1960's. The bases are designed around a metal stamping manufactured from copper-clad Kovar material. This material is typically 0.010" thick and consists of a layer of 0.007" Kovar physically bonded to a 0.003" layer of copper. The Kovar alloy is a preferred material to bond to the glass employed, while the copper layer provides the properties required for a reliable cold-weld seal to the cover.
Cold-weldable bases for the electronics industry in general, and the frequency-control industry in particular, have been manufactured for over thirty years. These bases (Military types HC-35, 37, 42, and 43 for example) are 0.100" high. This height is necessary to provide a thickness of glass sufficient to effect a hermetic seal while providing a decoupling area in proximity to a flange where the cold-weld is effected. This decoupling area is intended to allow the movement of metal that occurs when the base and cover are cold-welded. Without this glass-free decoupling area, mechanical stresses from the cold-welding operation would crack and destroy or compromise the hermeticity of the completed component.
Applicant is aware of the following U.S. Pat. Nos.: 2,444,312; 2,976,465; 3,184,534; 3,419,763; 3,546,363; 3,726,987; 3,816,847; 4,706,106; 5,206,460; and, 5,367,124.